1. Field of the Invention
The present invention relates to the field of space and more particularly to one or more spacecraft able to control the solar pressure to which they are subjected by means of a solar sail.
2. Description of the Prior Art
Designs for satellites intended to fly in formation to detect planets outside the solar system are known in the art. These formation flights necessitate a plurality of satellites (typically six satellites) with extremely tight relative positioning demands. Other types of constellations are envisaged in the field of astronomy for synthetic aperture imaging, simulating a mirror with maximum dimensions that correspond to the maximum distance between two satellites (which is typically of the order of several hundred meters). These dimensions are obviously not compatible with the diameters available under the nose-cap of current launch vehicles (typically a few meters) and therefore represent a major technological leap. The orbit for this type of application is generally selected from orbits at the Lagrangian points (typically the L2 point), because of the extremely stable nature of the conditions (thermal, gravitational, radiation) that apply to these orbits, enabling the embarkation of highly sensitive and cooled payloads. In terms of formation flying performance, this implies micrometric or even nanometric accuracy and stability over relatively long time periods (up to a few days).
Controlling formation flying and deploying complex structures in orbit require intersatellite propulsion means (actuators) that are highly accurate (providing a thrust from a few micronewtons to a few millinewtons) at the same time as minimizing accommodation constraints (mass, reliability, no obstruction of the fields of view, no plumes, no pollution of the optics, etc.). In Lagrangian point orbits and orbits sufficiently far from the Earth (typically at distances greater than 100 000 km), the dominant disturbing forces and torques are caused by differential solar pressure between the satellites of the constellation and the torques generated on each satellite. This may also apply to a single satellite under similar conditions.
To satisfy the requirements cited above, the constellation must comprise a certain number of satellites, very accurate metrology subsystems, and propulsion subsystems for countering the solar pressure that are extremely accurate and generate very low levels of noise.
The concepts conventionally adopted to respond to this type of requirement are based on a constellation comprising n identical and autonomous satellites with propulsion based on a system of thrusters distributed over the entire constellation. The type of thruster used ranges from the standard chemical type to ionic thrusters and field electrical effect propulsion (FEEP) thrusters, the latter employing the application of high voltages to molecules of cesium or indium to generate a very high speed thereof for propelling the craft.
However, propulsion control systems using thrusters suffer from a certain number of problems, in particular pollution of the optics, noise, lack of accuracy of the thrusters, generation of plumes, accommodation on the satellite and increased mass, because of the presence of the thrusters.
Moreover, propulsion control systems using coils and wheels suffer from complementary problems, in particular microvibration of the wheels, noise generated by the wheels during operational phases, the service life of the wheels, the impossibility of effecting inertial correction as a function of the intersatellite distance of the constellation.
An object of the invention is therefore to provide a satellite intended to travel in a constellation of satellites in an area of space in which the dominant disturbing forces and torques are for the most part caused by differential solar pressure between said satellites of the constellation, said satellite being able to control its attitude when flying in formation without using thrusters or wheels, very accurately and with minimum induced noise.